Skimming apparatus



May 16, 1944. H, A. STAHL ETAL 2,348,938

SKIMMING APPARATUS Filed Jan. 50, 1941 2 Sheets-Sheet 1 May 16, 1944. H. A. STAHL ETAL SKIMMING APPARATUS v2 sheets-sheet 2 Filed Jan. so, 1941 Zfy- Patented May I6, 1944 SKIMMING APPARATUS Harold A. Stahl, Lansdo Philadelphia, Pa., assi wne, and Leo D. Jones, gnors to The Sharples Corporation, Philadelphia, Pa., a corporation of Delaware l'Application January 30, 1941, Serial No. 376,596

(Cl. 21o-51) 8 Claims.

The present invention pertains to the art of skimming liquids from the surface of a tank in which they are contained. It was conceived as a solution of problems arising in connection with the separation of solids in a gravity settling tank from a mixture of aqueous detergent solution and grease obtained from a wool scouring bath, and the object and nature of the invention may probably best be illustrated by a discussion of these problems.

In passing a mixture of detergent solution, grease and insoluble solids from a woolscouring bath to a centrifugal separator for separating the mixture into its constituents, it is desirable that at least a part of the dirt be first removed by gravity settling before the mixture is passed to the centrifugal separator. The mixture is therefore passed from the scouring bath to a gravity settling tank and from the gravity settling tank to the centrifugal separator. The conventional method of removing the mixture of aqueous phase and grease from the gravity 'settling tank to pass it to the centrifugal separator consists in the use of a swinging arm which is secured to a float in the settling tank. The liquid may pass through the skimming arm to a separate chamber or container which contains a column of the liquid balanced against the liquid in the swinging arm. In such an arrangement, as liquid is withdrawn from the chamber containing the balancing liquid column, liquid in the swinging arm descends and is replaced by liquid passing from the settling tank into the swinging arm.

In another form of apparatus in accordance withthe prior art, liquid is passed from the skimming arm directly to a centrifugal, without passing iirst to a balancing column of liquid. In such case, however, the cross-section of the liquid passage through the swinging arm or associated conduit is restricted'to prevent too rapid passage of the liquid to the centrifugal. This arrangement, like the balancing column of liquid, operate's on the principle of maintaining the skimming arm full of liquid during normal operation by providing a flow restriction on the'down-stream side of the skimming apparatus.

The arrangements described above give satisfactory results in cases in which the liquid phase of the material subjected to the settling operation is homogeneous. When a mixture of liquids, such as the mixture of oil and aqueous phase received from the scouring baths, is treated in such an apparatus, however, diiiiculty is encountered in withdrawing from the settling tank a mixture of liquids in substantially the same proportions as the mixture fed to the settling tank. In the treatment of our oil and grease mixture used for an illustration, a part of the grease rises to the surface, and the skimming arm has a tendency to suck the aqueous phase from beneath the layer of grease, leaving the supernatant and accumulating layer of grease in the settling tank.

Upon analysis of the problem, the applicants concluded that the reason for the objectionable phenomenon of removal of aqueous phase without removal of grease could be attributed to the low velocity of flow of liquid from the settling tank into theV skimming arm, this velocity not being sufiiciently great to draw the grease into the skimming arm along with the aqueous phase. Having appreciated the nature of the problem, the applicants have succeeded id solving it by devising an arrangement which prevents the flow of liquid into the swinging arm from being limited by a restriction down-stream. The liquid thus undergoes a substantial and sudden drop in passing from the settling tank into the skimming arm, with the result that the grease is carried along with the aqueous phase into the swinging arm, and that no grease layer accumulates on the upper surface of the settling tank.

As indicated above, the object of the invention has been to provide an arrangement by which liquid can be drawn at a controlled rate from a container, with a sudden drop of the liquid as it is withdrawn from the main body of the container into the skimming arm or other floating skimming apparatus, thereby avoiding retention of a stratixed layer of lighter liquid in the container.

Further objects of the invention and the manner in which they have been attained will be evident from a reading of the following detailed description in the light of the attached drawings, in which,

Figure 1 is a side elevation, partly in section,

illustrating a settling tank, floating skimming member and supplemental skimming member controlling tank embodying the features of the invention,

Figure 2 is a plan view of the skimming tank, controlling tank, and connections between these tanks,

Figure 3 is a plan view of the weir box and iloat and associated parts of the invention.

Figure 4 is a cross-section on the line 4--4 of Figure 3, and

Figure 5 is a diagrammatic view illustrating a detail of an alternative embodiment of the invention.

The invention is illustrated in the drawings as applied to a settling or storage tank l0 having conical chambers Il on its under side to receive deposited solids. A float I2 is mounted on a skimming arm I3 which is pivoted at I4 and` the oat I2 and associated skimming arm I3 may swing through a fairly wide arc, as indicated by the full line and dotted line positions, respectively, of Figure 1 of the drawings. A weir box I8 is secured to the upper part oi' the float I2 and includes a weir I9 across which the liquid ows in passing from the surface of liquid in' the tank I into the swinging arm I3.

An air conduit, which may consist of a rubber hose connection 23, is secured to the closed upper end of the float I2, and this conduit is connected by means of piping 2| to a container 2 2 which is held in inverted position above the liquid in the bottom part of the chamber I6, and which will accordingly be referred to hereinafter as a bell. A discharge conduit 24 is secured to the bottom part of the chamber I6, and a pump 25 may be provided to remove liquid throughk the conduit 24 from that chamber. A feeder conduit 23 communicates with the conduit 2| and serves to admit air under pressure through a throttle valve into the conduit 2I in order to replace air which may be lost from the system.

In the operation of the apparatus, when liquid is fed to the tank I0, and rises in this tank, a part of this liquid will enter the oat I2 through the opening I1 in the bottom of the iloat, and the weir I9 will accordingly be held below the surface of the liquid in the tank. Liquid will accordingly flow across the weir I9 into the skimming arm I3 and will drop through this arm and the conduit I5 into the supplemental chamber I6. As the liquid rises in the chamber I6, the surface L of this liquid will extend upwardly beyond the lower end of the bell 22, with the result that the air in the interior of the bell 22 and associated conduits 20 and 2l will be compressed. As the super-atmospheric pressure on the interior of the bell 22 and in the conduits and 2| increases, the level L of the liquid in the chamber I6 surrounding the bell will be higher than the level L' within the bell, this dill'erence in level being proportional to the pressure. As the pressure in the bell 22 and conduits 20 and 2| increases, air will be forced into the upper end of the iioat I2, with the result that a part of the liquid will be forced out of this oat through the opening I1 in the bottom of the oat. This forcing of liquid out of the iloat will cause it to rise and carry the weir I9 upwardly to a point at which liquid no longer flows across this Weir into the skimming arm I3 and chamber I6. As liquid is withdrawn from the chamber I6 through` conduit 24 by pump 25, the pressure on the interior of the bell and in conduits 20, and 2l will again diminish, with the result that liquid will re-enter oat I2 through opening I1, causing this float to again descend in the body of liquid in the container Ill until the weir I9 is below the surface of liquid in the container I0, and the skimming operation will be resumed when this occurs.

From the above discussion it will be seen that the invention provides an arrangement by which the skimming of liquid from the container I0 is assaose correlated with, the rate of passage of liquid through the conduit 24 from the. container I3 and chamber Il, but that liquid does not aocumu late in the skimming arm I3 as in the prior art, but passes swiftly to a lower level. thereby enabling the skimming member I3 to act as a true Weir across which the liquid drops swiitly into skimming arm I3 to a level much lower than the level of liquid in the container I3. As the result oi' this swift drop of the liquid, the objectionable phenomenon of retention of a lighter stratum oi liquid in the container I3 is entirely avoided.

An alternative form of the invention is ilimtrated in Figure 5 of the drawings. In this form of the invention, a oat 30 is secured to a swinging arm 3i, and an opening 32 is formed in the under side of the iloat to permit entry of water into the float in the same manner as discussed above in connection with the embodiment of Figures 1 to 3 of the drawings.

A weir `box 33 is secured to the float 3l, and the weir box 33 is made suiiiciently large to oonstitute a supplemental chamber which fulfills a function similar t0 that of the chamber I3 of the embodiment of Figures 1 to 3. A float 33 is mounted in the supplemental chamber or weir box 33 and is secured by a connection 34 to a three-way valve 35 which controls the admission of air from a conduit 33 into the upper end of the float 30. As in the embodiment of Figures l to 3 of the drawings, liquid flows across a weir 31 from the main body of liquid in the container (not shown) corresponding to the container III of Figure 1 of the drawings. In the operation of this device, the valve 33 ls maintained in communication with the atmosphere during the normal operation of skimming liquid across the weir 31 into the weir box 33. In case the liquid skimmed across the weir 31 is accumulated in the weir box 33 at a faster rate than the removal of liquid from this weir box, the level of liquid in the weir box 33 will rise, and this level, operating through the float 33 and connection 34 will ultimately actuate the valve 3l to move it to a position in which air under pressure is admitted through conduit 33 Vinto the upper end of oat 30. This will cause a part of the liquid in the bottom of the float 33 to be expelled through the opening 32, with the result that the oat 30 will become more buoyant and will rise to a point at which the weir 31 is above the liquid level line of the tank. This weir will be held in this elevated position by the buoyancy of the float 30 until suilicient liquid is withdrawn from the supplemental chamber or arm to cause the level of liquid in the Weir box 33 to recede to such point as to cause the float 33, operating through the connection 34, to move the valve 3l to a position in which air is released from the upper part of oat 30. When this occurs, liquid again enters the float 36 through opening 32, causing this float to descend and drawing the weir 31 into a position below the surface of liquid in the tank.

It will be seen that, in the embodiment of Hgure 5 of the drawings, as in the embodiment of Figures 1 to 3, the invention provides an arrangement by which liquid passing from the tank across the weir undergoes a substantial drop,

thereby insuring that the lighter, as well as the heavier, liquid will be skimmed from the tank.

It will be seen from the above discussion that the fundamental features of the invention oonsist in the following steps. Means are provided for skimming liquid over -a weir from the surface of liquid in a container. 'Ihe liquid is to a separate container, The level of the weir"in the liquid in the first container is controlled by the quantity of liquid in the second container. Thus, if the quantity of liquid in the second container becomes too great, by reason of failure to withdraw liquid from this second container as fast as it is passed to the second container from the rst container, the weir will automatically be moved upwardly in the iirst container to lift the upper edge of the weir above the level of liquid in the first container, or at least to decrease the degree of immersion of the weir. If, on the other hand, the level of liquid in the second container descends, the Weir will be moved downwardly in the first container to cause liquid from the first container to be withdrawn across the weir into the second container.

Still further modifications will be obvious toy those skilled in the art, and we do not therefore wish to be limited except by the scope of the following claims.

We claim:

1. In an apparatus for skimming liquid from the surface of liquid in a container, a Weir mounted for immersion beneath the surface of said liquid and for upward and downward movement in said container. a supplemental chamber mounted in position to receive liquid discharged over said Weir, means for directing liquid discharged over said weir into said supplemental chamber, fluid actuated means connected with said weir to eiect upward and downward movement of said weir in said container to change the vertical position of said weir relative to the surface of liquid in said container, a fluid conduit operatively connected to said weir actuating means, and means responsive to accumulation of liquid in said supplemental chamber for increasing the fluid pressure in said conduit and effecting the operation of said means for changing the position of said weir upwardly relative to said liquid surface upon accumulation of liquid beyond a predetermined amount in said supplemental chamber.

2. In an apparatus for skimming liquid from the surface of liquid in a container, a Weir mounted for immersion beneath the surface of l-iquid and for vertical movement in said container, a float having an opening in its lower end secured to said Weir, a second container mounted in position to receive liquid discharged over said Weir, means for directing liquid discharged over said Weir into said second container, a bell mounted in said second container in a position in which its open lower end is adapted to be immersed in liquid accumulating in said second container, and a pneumatic connection between the closed upper end of said bell and the upper portion of said oatin said first container, whereby accumulation of liquid in said second container effects compression of air within said bell and forces said air from said pneumatic connection into said iioat and thereby expels liquid through the open lower end of said float to increase the buoyancy of said float.

3. In an apparatus for skimming liquid from the surface of liquid in a container, a weir mounted for immersion beneath the surface of said liquid and for vertical movement in said container, a supplemental chamber mounted in position to receive liquid discharged over said weir, means for directing liquid discharged over said Weir into said supplemental chamber, operating means for effecting vertical movement of said weir, pneumatic means interconnecting said supplemental chamber with said operating means for -eifecting vertical movement of said weir, and

means responsive to accumulation of liquid in said supplemental chamber beyond a predetermined amount for transmitting pressure 'energy through said pneumatic connection to said operating means, said operating means being controlled by transmission of said pressure energy for moving said weir upwardly relatively to the liquid surface in said container upon accumulation of liquid beyond a predetermined amount in said supplemental chamber.

4. In an apparatus for skimming liquid from the surface of liquid in a container, a weir mounted for immersion beneath the surface of said liquid and for vertical movement in said container, a float having an opening in its lower end secured to said weir, a second container mounted in position to receive liquid discharged over said weir, means for directing liquid discharged over said weir into said second container, pneumatic means interconnecting said second container with said float and means responsive to accumu- 4 lation of liquid in said second container beyond a predetermined amount for transmitting pressure through said pneumatic connection to said float, whereby gas is forced into said oat to cause movement of said oat and Weir upwardly relative to the liquid surface in said rst container upon the accumulation of liquid beyond a predetermined amount in said second container.

5. In an apparatus for skimming liquid from the surface of liquid in a container, a Weir mounted for immersion beneath the surface of said liquid and for upward and downward movement in said container, a supplemental chamber rigidly associated with said Weir and mounted to oat within said container in position to receive liquid discharged over said Weir, means connected to said supplemental chamber to effect Vertical movement of said supplemental chamber and said weir in said container to change the upward and downward position of said weir relative to the surface of liquid in said container, a float in said supplemental chamber, and means actuated by said float in said supplemental chamber for controlling the operation of said means for changing the position of said weir relative to said liquid surface in said container, said supplemental chamber being provided with an outlet for discharge of skimmed liquid therefrom.

6. In an apparatus for skimming liquid from the surface of liquid in a container, a Weir mounted for immersion beneath the suriacefof said liquid and for upward and downward movement in said container, a supplemental chamber rigidly connected with said weir and mounted to float within said container in position to receive liquid discharged over said weir, pneumatic means connected to said weir to effect vertical movement of said weir in said container to change the upward and downward position of said weir relative to the surface of liquid in `said container, a float in said supplemental chamber, and means actuated by said oat in saidsupplemental chamber for controlling the operation of said pneumatic means for changing the position of said weir relative to said liquid surface in said container, said supplemental chamber being provided with an outlet for discharge of skimmed liquid therefrom.

7. In an apparatus for skimming liquid from the surface of liquid in a container, the combination comprising a skimming arm comprisinga conduit for discharging liquid from said container, a weir connected to said skimming arm for controlling the iiow of liquid -into said conduit and mounted for immersion beneath the surface 'of liquid in said container, a float having a hole in its underside and secured to said arm and supporting said weir, a conduit connected to the upper pJttion of said float, and means renderedv operative by liquid Passing over said weir for varying the pressure of air in said conduit and the upper portion of said tioat to cause said iioat to move relatively to the level oi liquid in said container.

8. In an apparatus for skimming liquid from the surface of liquid in a container. the combination comprising a arm comprising a conduit for discharging liquid from said contain-.

er,aweirconnectedtosaidakimmingarmtor continuing the now of liquid into said conduit and mounted for immersion beneath the surface of liquid in said container, a iioat having a hole in its under side and secured Vto laid arm and supporting said weir, a conduit connected to the upper portion or said float, a receptacle mounted to receive liquid discharged over said weir. and means rendered operative by accumulation of liquid in said receptacle for varying the pressure oi' air in said conduit and the upper portion of said iioat to cause said iioat to rile reiatively to the level of liquid in said container, said receptacle being provided with an outlet for discharge of skimmed liquid.

HAROLD A. STAHL.

LEO D. JONES. 

